Significant advances have been made in applications using 630 nanometer band AlGaInP (aluminum gallium indium phosphide) red semiconductor lasers (laser diodes: LD) in display devices because of good visual characteristics such as high brightness. One important application of these semiconductor laser diodes (Hereafter, called laser diodes) is projecting a laser beam onto an object for visual recognition in display devices such as markers and levelers. Since portability is a highly important condition, battery power is a main requirement. The laser diode must therefore consume as little electrical power as possible in order to allow long term operation from batteries. A high quality laser beam is also an essential element when using the laser diode as a display device.
One method effective in lowering the laser diode drive current is to use a semiconductor device with a real index guided structure possessing highly efficient light emission with minimal internal (waveguide-cavity) loss in the laser diode device. Structures of this type are disclosed (for example, in JP-A No. 2002-353566), where the conventional laser diode with a buried layer of GaAs (gallium arsenide) is replaced with a buried heterostructure laser diode of Al(Ga)InP (aluminum gallium indium phosphide) with extremely low light absorbance; and a ridge type laser diode (for example JP-A No. 2006-165407 and International Publication No. WO 02/101894) that utilizes the ridge side surface of the dielectric layer as a protective layer instead of a buried layer.
The semiconductor laser diode disclosed in JP-A No. 2006-165407 is formed with a structure to prevent light in the ridge section from leaking outside the laser by forming a facet (forward emission side) for emitting laser light, or a groove in the vicinity of the facet, or a concave section. This structure is capable of preventing ripples in the FFP (far field pattern) intensity distribution, and acquiring Gaussian shapes with good FFP.
The semiconductor laser diode disclosed in International Publication No. WO 02/101894 contains a facet including at least an active layer cross section the surface of the active layer prevents ripples from occurring in the FFP and acquires Gaussian shapes with good FFP.